1. Field of the Invention
The present invention relates to a resistance temperature sensor, and more specifically to a resistance temperature sensor such as a platinum temperature sensor which makes use of the property that the resistance value of the resistance material changes dependent on temperature.
2. Description of the Background Art
FIG. 14 shows a conventional resistance temperature sensor 50 of interest to the present invention.
The resistance temperature sensor 50 comprises an insulating substrate 51 formed of alumina, on which a resistance circuit pattern 52a of platinum is formed. The resistance circuit pattern 52a is formed in the following manner.
A resistance film 52 of platinum is formed on the entire surface of the insulating substrate 51 by vapor deposition, sputtering, or printing and baking of a platinum paste, then grooves 53a are formed by dry etching, chemical etching or laser cutting, and thus a resistance circuit pattern 52a is formed in a zigzag pattern as shown in the figure. Grooves 53b are formed in the resistance film 52 along the peripheral edge of the insulating substrate 51 by a similar method. Even if the resistance film 52 peels off from end portions of the substrate, the peeling of the film is prevented at the grooves 53b, and thus the grooves 53b serves to prevent further peeling.
Terminal electrodes 54a and 54b are respectively formed by the resistance film 52 on the left and right sides of the resistance circuit pattern 52a. Conductive films 55a and 55b of gold, for example, are respectively formed on the terminal electrodes 54a and 54b. External terminals 56a and 56b formed of, for example, platinum clad wires are connected to the conductive films 55a and 55b by, for example, welding.
Portions of the external terminals 56a and 56b connected with the conductive films 55a and 55b may be coated with reinforcing layers 57 made of glass, for example, so that the connecting portions of the external terminals 56a and 56b are reinforced. Although the reinforcing layer 57 is not shown on the external terminal 56a on the left side, actually that terminal may also be coated with a reinforcing layer in the same way as the external terminal 56b on the right side.
Although not shown, a protective coat is formed on the insulating substrate 51 on which the resistance film 52 and the like are formed. The protective coat is formed of resin or glass, for example. It protects the resistance film 52 from moisture, waste, dust and so on and physically reinforces the resistance film 52. The reinforcing layers 57 may be formed simultaneously with the protective coat.
In the resistance temperature sensor 50 of FIG. 14, the resistance film 52 is formed entirely on the insulating substrate 51, and the resistance circuit pattern 52a and the terminal electrodes 54a and 54b can be easily and effectively formed by dry etching, chemical etching or laser cutting, so that the time required for manufacturing can be reduced.
Generally, the resistance circuit pattern 52a of the resistance temperature sensor 50 is heated to a constant temperature by letting a current flow through the external terminals 56a and 56b. When a flow rate of air is to be measured, for example, the resistance temperature sensor 50 is positioned in the flow path of the air. When the flow rate changes, the thermal equilibrium state is changed, and the amount of change is measured by a known bridge circuit.
However, in the resistance temperature sensor 50 shown in FIG. 14, the resistance circuit pattern 52a and the terminal electrodes 54a and 54b are formed continuously, and in addition they are formed of a material having high heat conductivity such as platinum. Consequently, heat generated in the resistance circuit pattern 52a is readily transmitted to the terminal electrodes 54a and 54b, and further to the external terminals 56a and 56b. Consequently, heat is retained not only in the resistance circuit pattern 52a but also in the terminal electrodes 54a, 54b, the reinforcing layers 57, and the external terminals 56a and 56b, increasing the thermal capacity of the resistance temperature sensor 50 as a whole, so that the speed of response to a change in the flow rate becomes slower.